Pulse type multiplex communication system



Aug- 15, 949 v c. w. HANSELL 2,478,919

' PULSE T'P YELTIPLEX COMMUNICATION SYSTT`M Filed July 17. 1943 n A f 7 sheets-sheet 2 WM5 @furia azsf 0077007 vvvvv I-u- M INVENTOR.

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I I PULSE TYPE MULTIPLEX COMMUNICATION SYSTEM 7 Shets-Shnet 6 Filed July 1'1. 194:5

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Patented Aug. 1e, 1949 PULSE Tres Mtn-Tierart comrUNrcA'roN sYs'rnM Clarence W. Hansell, Rocky Point, N. Y., assigner to Radio Corporation of America, a corporation of Delaware Application July 17, 1943, Serial N0. 495,181

12 Claims. (Cl. Z50-9) The present invention relates to communication systems employing pulses of radio frequency energy which are short compared to the time intervals between them, and particularly to a multiplex system wherein a plurality of trains or groups of pulses are transmitted. each group bearing its own modulation in accordance with the particular message to be conveyed thereby.

4In my copending application, Serial No. 371,865, led December 27, 1940, nw U. S. Patent 2,381,444, granted August '7, 1945, there is disclosed a pulse type communication system in which the receiver is rendered operative solely at time periods when the signal pulses are due to arrive. I prefer to call a receiver operated in this manner a shuttered" or gated receiver.

Advantages of such a system are: (1) The peakA power at the transmitter can be made to exceed considerably that which is obtainable in a continuous wave system, by virtue of the fact that the transmitted power is concentrated in the short pulses, and (2) that there is obtainable an increase in the signal-to-noise power compared to continuous wave systems, not only because of the increased transmitted power but also because the receiver is responsive only during time periods which may be occupied by the transmitted pulses. thus eliminating the effect of noise and interference occurring between pulses.

In accordance with the present invention, there is provided a multiplex system wherein a multiplicity of transmitting channels are operated over a single transmitter to transmit nonoverlapping pulses which are very short compared to the time intervals between them. The train or group of pulses from cach transmitting station has its own modulation impressed thereon, and thepulses from all transmitting stations occupy only a small percentage of the total time for all conditions of modulation. The transmitter peak power is almost inversely proportional to the percentage of total time occupied by the pulses, and is thus high compared to known continuous wave systems. At the receiver, a synchronization system is employed to enable the different receivers or utilization circuits to be individually responsive at diierent times and solely at those times at which the signal pulses are due to arrive. Thresholding au.: limiting devices may be employed at the receiver to further reduce the noise. Thus, if there are continuous wave transmitters which might tend to interfere with the pulsing system of the invention, the output from the continuous wave transmitters must reach the receiver of the invention with greater strength to u Fig. 1;

. 2 y produce interference than with a continuous wave receiver. So long as the received strength of the continuous waves is less than the threshold value set at the receiver oi' the invention, the continuous waves will not interfere greatly with the operation of the present invention. Likewise, if the continuous waves do not modulate the signal current down to values below the limiting value they will not interfere greatly with the operation of the present invention. In general, so long as the peak amplitude oi all noise and interference combined is less than half the peak amplitude of the pulse signal, a very great reduction in the eifect of the combined noise and interference may be accomplished by the thresholding and limlting.

In accordance with the present invention, all

pulse transmitting stations of the multiplex system will operate from a single transmitter and have the same pulse or repetition rate, although t the different trains or groups of pulses from the stations will occupy separate time periods. A single receiver receives all the pulses, and by means of suitable switching or commutating circuits transfers the different trains of pulses to the diierent channels to render them responsive solely at times when these pulses are due to arrive.

An outstanding advantage for the pulse system of the present invention employing a shuttered or "gated" receiver is that great stability of radio frequencies in transmitter and receiver is not required. Therefore` the system is particulax-ly advantageous fo'r use at the highest radio frequencies where frequency stability provides a. serious problem in continuous wave systems. The discrimination against noise and interference made possible by the pulse rate and pulse timing selectivity replaces the selectivity based upon close control of radio carrier frequencies, which is relied upon in continuous wave systems.

A more detailed description of the invention will now be given, in conjunction with the drawing,wherein:

Fig. 1 schematically illustrates the transmittug end of a pulse type multiplex communication system, in accordance with the present inention;

Figs. 2 to 6 schematically illustrate details oi dulerent pulse delay er circuits which can be used in the transmitting Istem of Fig. 1

Figs. 7 and 8 schematically illustrate details of'difierent types or pulse modulation circuits which can be used in the transmitting system of Fig. 9 schematically illustrates the receiving end of a pulse type multiplex communication system in accordance with the present invention:

Fig. l schematically illustrates the details o! a pulse controlled switcher circuit which can be used in the receiving system of Fig. 8; and

Figs. 11 and l2 show cliierent embodiments of individual receivers for receiving and demodulating pulses sent out from a remote transmitter.

Referring to Fig. l, there is shown in block diagram a pulse type multiplex transmitter suitable for the transmission or pulses which are modulated in length or timing. This transmitter includes a pulse keyed radio frequency amplifier IQ which is supplied with radio frequency excitation from a constant radio frequency oscillator I I. Transmitter In is provided with vacuum tube keying equipment capable of causing the transmission of very short pulses of radio frequency energy in response to short input pulses. The output from the transmitter i6 passes over a suitable transmission line l2 to an antenna system I3, here sho an, by way of example only, as a directive antenna in the form of a parabolic reflector having a dipole at its focus. A pulse oscillator I4 produces pulses at a constant rate, which pulses are short compared with the time spacing between them.

These pulses are repeated at a frequency above the highest modulation frequency, and are delivered to pulse modulators i5, I6, Il, etc. and to a pulse delayer 20. The pulse modulators i5, IS and Il have respectively impressed thereon modulation inputsv from leads l5', I6 an Il', in order that the outputs of these modulators consist of trains or groups of pulses suitably modulated in accordance with the intellgence to be conveyed on the different channels. The outputs from the pulse modulators I5, I6, I'I, etc. are respectively delivered to pulse delayers rnd keyers 2i, 22, 23, etc. These pulse delayers are adjusted for diierent delays in order to provide pulses which constitute the input to the transmitter or pulse keyed radio frequency amplifier I3. The pulses delivered to the transmitter lil from the delayer circuits are preferably equally spaced in time, on the average, and recur at a pulsing rate equal to the rate oi the pulse oscillator i4 multiplied by the number of pulse delayer modulators plus one. Obviously. the pulse outputs from the different channels (each of which includes a pulse centers of continued pulses will be micro-seconds. The pulse length may be on the order of a. hal! micro-second. For this example, it will be evident that the percentage ofv time occupied by all pulses in each cycle of operations for all condltions o! modulation may be only 2.5% of the total elapsed time, as measured from the begin- A ning of one pulse transmitted by the rst chan- Y layer and keyer 20 without the intermediary of a pulse modulator' circuit. This arrangement is preferred because it is desired that the pulses from the output of the pulse delayer 2li be the rst ones recelvgd at the receiver, and these pulses employed to synchronize or render operative the various receiving circuits solely at those time pe-' riods when lthe signal pulses for the respective channels are due to arrive. In view of the slight delay occasioned in the system of the invention in rendering the receiving circuits sequentially operative after the receipt of the rst pulse. it is preferred that there be no modulation impressed on the synchronizing pulses, in accordance with the preferred embodiment of the present invention. This feature will be described in more detail later in connection with the receiving system of Fig. 9.

Figs. 2. 3, 4, 5 and 6 show different types of pulse delaying circuits which can be employed in the system of Fig. 1.

Referring to Fig. 2 in more detail, there is shown a triode vacuum tube 30 to whose grid is supplied an input pulse through a transformer 3|. A positive polarizing potential is supplied to the anode of the vacuum tube through a. variable resistor 32 and the primary winding of a transmodulator and delayer circuit) are independently modulated for the transmission of independent programs or modulations.

The pulse delayer circuits 2U, 2l, '22, 23, etc. pass pulses at the same repetition rate as the pulse oscillator il but at different times. Thus. if the pulse modulator circuits modulate the length or the pulses, for example, the transmitter will send out constant irequeztcP but variable length pulses separated in time. l?, however, the pulse modulators modulate the timing of the pulses, the transmitter Ill will send out timing modulated pulses Whose average frequency is tie same but which are retarded or advanced in time by the modulation. ,Y

The pulses from each delayer circuit are short compared to the time intervals between them, in order that the pulses from all the channels occupy oni:T a small percentage of the total time for all conditions of modulation. Thus, as an example, a 5 channel telephone multiplex system including a synchronizing channel might have a pulse rate In each channel of 10,D0l per second, :n which case the average spacing between former 33. A condenser 34 is connected between the cathode of the triode and the junction between the resistor 32 and the primary winding oir the transformer 33. In circuit with the cathode as shown, there is provided a condenser 35 which is shunted by a resistor 36 whose adjustment provides the desired delay between the input pulse and the output pulse. The time delayed output pulse is taken .from the secondary winding of the transformer 3". Vacuum tube 30 is so biased that it is normally conductive (that is, passes anode current in the absence of an input pulse). In

this condition, a current will flow from the positive vpolarizing source through the resistor 32 and through the pri nary winding of transformer 33, thus shunting or by-passir.g condenser 34. An incoming pulse applied to the transformer 3i will drive the grid of the triode momentarily positive to charge the condenser 35, due to grid rectiication, as a' result of which a negative charge is placed on the grid of the tube 30, thus biasing the tube and rendering it non-conductive. When the ttoe 30 becomes non-conducting, current will flow from the positive anode polarizing sourcethrough the condenser 3d to ground, and will thus charge the condenser 34. When the charge on condenser 35 leaks of. through its shunt connected resist-or 36, the grid will approach a state of zero potential relative to the cat-bode, at which time the tube 3c will pass current, thus enabling the condenser 34 to discharge across the tube. A pulse is thus a. xs passed through the transformer 33 whose time of occurrence is controlled by the adjustment of the grid resistance 36, the latter determining the length of time it takes for the charge on conto Fig. 2. except that the vacuum tube en' is a screen grid tube and the condenser 34' is in the y screen grid circuit. The elements which are common to Figs. 2 and 3 have been given the same reference numerals, and this applies to Fig. 4 also. Since condenser S4', resistor 32' and racuum tube 30' of Fig. 3 respectively serve the same purpose as condenser 34, resistor 32 and vacuum tube 30 of Fig. 2, they have been given the same reference numerals except for the prime desig tions. Tube 30' is normally conductive and except for the structural differences hereinabove noted, the operation of Fig. 3 is substantially the same as the operation of Fig. 2.

Fig. 4 is an arrangement similar to Fig. 3, with the exception that there are employed in Pig. 4 two condensers 34 and 34 which charge and discharge simultaneously, thus providing aharper output pulse from the transformer 33. It should be noted that eondensers 34 and 54 are connected to the positive polarizing potential through separate resistors 32 and 32', respectively. Except for the structural differences noted, the operation of Fig. 4 is substantially the same as that of Pigs. 2 and 3.

The pulse delay circuit of Fig. 5 includes a triode electrode structure 40 and a diode electrode rig 6,1m@ triode lo' is so biased as to be normally non-conductive (that is, it passes no current in the absence of an applied pulse to transformer 3l). The application of a. pulse to the transformer 3i will cause a rectified current in the output of the diode 4l which will charge the condenser 35 in such manner as to apply a positive charge on the grid of triode 4U' through one winding of the transformer 4Z'. This positive charge on the grid of the triode will cause the triode to pass current until such time as the charge on condenser 35 .leaks oil` through its shunt connected resistor 36 down to some lower value. at which time the curr ent through the triode begins to reduce. Due to regeneration from the transformer 42' (by virtue of the feed-'rack path shown) the triode 4D' cuts itself off suddenly and passes a pulse through to the output circuit. It will thus be seen that the system of Fig. 6 works in reverse compared to the system of Fig. 5. Certain renements shown in Fig. 6 which are not shown in Fig. 5 include the condenser and resistor 46 combination in the anode circuit of the triode. The condenser 45 and the main inductance oeil in the anode circuit of the triode 40' may, if desired, be adjustable for coarse time delay adjustment, whereas the adjust- 'ment of resistor 36 provides exact time delay adjustment. The resistor 46 can be replaced by a is shown a triode vacuum tube across whose grid structure 4| which, although shown in separate envelopes. may, if desired, be included within a single envelope. The triode 40 is normally conductive (that is, passes current in the absence of an input pulse applied to transformer 3l) During the conductive condition of tube 0. the condenser 43 which is connected across the cathode and anode through a winding of output transformer 42. is shuntsd out or tay-passed The rectier 4| passes current upon the application of an input pulse to transformer 3l, as a result of which the condenser 35 will become charged and apply a. negative bias to the grid of the triode 40, thus biasing the triode 4l to the anode current cut-oil' condition. When triode 40 becomes nonconductive due to the negative charge on condenser 35, the condenser 43 will become charged. After the charge on condenser 35 leaks oil* through its shunt connected resistor 36, the triode 4U will again pass current, at which time the ccndenser 43 will discharge through the triode 4b and pass a pulse through the transformer 42. In order to sharpen the output pulse, a. feed-bari path is provided between the transformer A2 and the grid circuit by means of the Winding L. This, when condenser 43 starts to discharge. the puise through transformer 42 will apply a positive impulsa to the grid of the triode 40, to cause the triode to pass current and discharge the oondenser 43 quicker than would otherwise be possible.

and cathode are connected a circuit 5l which extends to the pulse oscillator i4 of Fig. l, and also a modulation input circuit 52 which extends to the source of modulating potentials for impressing modulations on the pulses in accordance with the intelligence to be conveyed. The modulation in- Y put circuit 52 is connected to the grid and cathode a pulse limiter i .s anode circuit of triode 50 includes an indu. tance 54 which stores energy therein, which entity is controlled by the tube anode current for delivery to the pulse delayer and pulse timing modulator vacuum tube 31V.

The control grid of vacuum tube 30' is connected to the anode of the vacuum tube 50 through a condenser 56. A condenser 34 is connected between the cathode and anode of the pulse delayer 30', while a condenser 34' is connected between the screen grid and cathode of tube 30 in substantially the same manner as the same numbered elements of Fig. 4. It should be noted that the condensers 34 and 34 have individual resistors 32 and 32' connected between them and the positive anode polarizing potential. An adjustable resistor 51 is connected between the cathode and control grid of tube 30 for providing an adiustment of average pulse delay.

In the operation of Fig. "i, the triode 5U ls normally conductive and stores energy in inductance 54. When a negative pulse fro` the oscillator I4 is applied to the circuit 5l and thence to the grid of the triode. the tube 50 wil' 2'; '1e its current cut od and cause the application of. a positive puise to the control grid of the tetrode 30'. The tetrode .Sll' is normally conductive the absence of Fig. 6 shows another embodiment of a pulse delay circuit which employs a triode electrode strucpulses. The application of a. positive pulse to the -zrelative to the input pulse.

afname ilcation which will charge condenser Sl negatively on the side adjacent the control grid of the tetrode 30'. The tube 30' is thus lcit in an anode current cut-ot! condition. During this condition, the condensers 34 and 34' charge up, and both of these condensers will discharge through the tube 30' when the negative charge on condenser 56 leaks od. The operation of vacuum tube 36'. it will thus be seen, is substantially similar to the operation of Fig. 4 previously described. For modulation purposes, the input to the trode 50 through circuit 52 and transformer 53 will vary the average bias of the triode amplifier and in this manner vary the energy stored in inductance L and the strength o! the pulse delivered to the tetrode, as a result of which the peak charge on condenser 58 will be varied in accordance with the modulation, thus varying the time delay of the output pulse It should be noted that the energy stored in coil 54 is delivered to the delayer tube 30 at each pulse. The anode current in the tube 50 should, of course. reach a substantially steady state value before each pulse. .Li desired, there may be provided a feed-back regenerative circuit in the tetrode circuit or in a later stage to sharpen the output pulse.

The system of Fig. 8 shows a p se modulation circuit which may be used in the system of Fig. 1 for modulating the length of the pulses. This circuit of Fig. 8, like that of Fig. 7, includes both the pulse modulator and the pulse delayer. In addition, the system of Fig 8 includes a pulse peak limiter tube 62 which follows the pulse delayer and length modulator Sil' in order to convert variable amplitude pulses from the output of the delayer tube to variable length pulses. The pulse delayer and length modulator herein represented by vacuum tube tctrode 30', with its l associated elements, is substantially the same as that shown in Fig. 7. It should be noted that in Fig. 8 the pulse input circuit 5I is applied between the grid and cathode of pulse amplifier tetrode vacuum tube 6D. The screen grid and cathode of tube G are connected together through a by-pam condenser 64, in turn shunting a portion of a potentiometer circuit 65. The modulation input circuit 52, however, is applied in Fig. 8 to a transformer 6I, which is connected in such manner that the anode supply voltage of tetrode 30' is modulated in one senseA while 'the control grid-cathode potential of tube 30' is modulated in an opposite sense for the purpose o! balancing the eiect of the module-'ion upon the time delay. I am thus able to obtain pulses of variable amplitude from the delayer tube 31)', which after being limited in pulse peak limiter tube S2 appear as pulses of variable length in the output circuit 63. The pulse amplier and limiter tube 60 is normally conductive in the absence oi a negative input pulse from the oscillator i4 applied to circuit 5I. The application of a negative pulse, to tn. ci.cut 5l serves to cut 0E the anode current in tube S0 momentarily, as a result of which a positive pulse is delivered into the dclayer tube 30 to produce grid rectication. The elements appearing in Fig. 8 which correspond in function to those in Fig. '7 haveY been given the same reference numerals.

Fig. 9 shows in block form a multiplex receiving system for use in receiving the multiplicity oi short duration pulses of received energy sent out by the multipex transmitter of Fig. i. The receiver includes an antenna 10 which is indicative of any sull able nei-gy collecting device which may be directive, a heter'idyne detector 1l which B i may, if desired, be preceded by a radio frequency amplifier, which is fed with energy from tha antenna 10 and also with oscillations irom l. local heterodyne oscillator 12, and an intermediate frequency amplifier 13 in the output oi tho heterodyne detector 1|. The intermediate irequency amplifier 13 has its output connected over leads 15 to a pulse keyer 1.5, and also over leads 18 to a multiplicity of other pulse keyers 11, 13, 19, etc. The pulse keyers 11, 1B, 19, etc. are associated with different communication paths or channels for receiving the dierent trains or K groups of pulses, each of which has its own modulation. The pulse keyer 15, on the other hand,

forms part of a pulse synchronizing system synchronized mainly by the end of the received nection with Fig. 10, operates in synchronism i' with the rst train of received pulses in response to the received pulses.

The different channels or communication paths in which are found the pulse keyers 11, 18 and 19 etc. are fed by pulse keying control currents over individual puise delayer circuits 81, 88, 89, etc., the latter in turn being fed over leads 85 from the output oi the pulse synchronized pulsing oscillator and amplifier S2. The pulse delayers .'51, 88 and 89 etc. have different delays which are adjusted to correspond to the average time spacing of the diierent series of incoming pulses. The outputs from 'the pulse keyers 11,

' 18, 19 etc. are respectively passed on to pulse integrator and demodulator circuits 81, S8, 99 etc. for reproducing the signal modulation. These pulse integrators and demodulator circuits are preferably biased to provide acertain threshold value below which no signal will be passed on to the subsequent utilization circuit, as an aid in eliminating noise and interference below the threshold value. The type of pulse integrator circuit will, of course, depend upon the type of modulation on the incoming pulses.

The outputs from the pulse integrator and demodulator circuits 91, 98 and 99, etc. are passed on respectively to audio amplifier and volume control circuits H11, ID3 and H79, from which the audio output is utilized in any suitable audio translating device such as a headphone, loudspeaker, recorder or printer.

Briefly stated, the operation of the pulse type multiplex receiver of Fig. 9 is as follows: The extremely short pulses sent out by the transmitter of Fig. 1 and which occupy a small percentage o! the total time, are received on antenna 10 and reduced in freouency in heterodyne detector 1l. and amplie. by intermediate frequency amplifier 13. The intermediate frequency signals from amplifier 13 pass through the pulse keyer amplier tube l5 whose output is rectified by 9| and the rectified pulse passed on to the synchronized pulsing oscillator 92, which. in turn. Lnterrupts the pulse keyer 15 at the frequency oi the rst series of received pulses. This first series of received pulses. in accordance with the preferred embodiment oi the invention. is passed by the pulse delayer and keyer circuit 20 of the transmitter of Fig. l and thus has no modulation.

The output pulses from the pulse synchronid pulsing oscillator 92 passes through the puise delayer circuits 81, 88 and 89 whose delays are adjusted to correspond` to the time spacing of the dierent series of incoming pulses, each series of which represents s. different channel and has its own modulation. The signals themselves, however, pass from the output of the intermediate and the length of gate open periods for each channel are made only large enough to include the desired pulses when they are modulated. The signals passed on by the pulse keyers in the different commulication paths or channels are' then demodulai'rd in the apparatus 91, S8. 99. etc.. the audio output of which is then amplied in audio amplifiers |81, |08, |09.

The synchronization system in the multiplex receiver of Fig. 9, which operates in synchronism with and under 'control of the received pulses. is illustrated in more detail in Fig. 10, whose elements bear the same numbered reference numerals as the corresponding elements in Fig. 9. Referring to Fig. 10. it will be noted that pulses of radio .frequency energy from the intermediate frequency amplifier I3 are applied between the grid and cathode of thepulse keyer l5 through a transformer H0. The pulse keyer 15 is normally biased to cut-o by virtue of a negative potential applied to the grid over a. path including a resistor 2 and a secondary winding of transformer HU. The output from the pulse keyer is applied to apparatus 9| which includes a rectifier and a direct current amplifier, as

shown.

It should be noted that the grid and anode circuits of the pulse keyer 'l5 comprise parallel tuned circuits. These tuned circuits are tuned to the intermediate frequency signal. The pulse synchronized pulsing oscillator and amplifier 92 is shown as a triode of the feed-back or regenerative type. The grid includes an inductance coil Hi which is coupled to the feed-hack coil ||2 in the anode circuit of the tube, both oi these coils, in turn, being coupled to another coil ||3 which passes positive pulses at the frequency of the pulse oscillator to the grid of the pulse keyer 15 over lead ||4 and resistance ||5. The oscillator 92, in effect, is a sew-tooth oscillator which normally operates by itself at a frequency slightly lower than the pulse rate of the incoming pulses. but is constrained to operate at the pulse frequency by the incoming synchronizing pulse sig- Th: values of the resistors and condensers either in the grid or plate circuits, or both, of the pulse oscillator 92 determine the frequency ol the oscillations ci' the pulse oscillator 9i. and these values together with the constants of the trans- Lern-1er in the oscillator circuit determine the length oi' pulses across resistance |2|, which are preferably equal to, or somewhat longer than the transmitted pulses. 'I'he voltage across the anode condenser ||6 and across the grid condense: H1

passed by coil I I3 is a short pulse wave. `Oscilla- I tor 92 operates continuously whether or not incoming signals arrive at the receiver. It is made relatively highly stable in operation. This type of pulsing oscillator. it will be recognized, is well known in the television art. .It will be found described in my. Patent #1,898,181 and in Toison and Duncan Patent #2,101,520. In the operation of the synchronization system. the incoming pulses applied to transformer H6, which are at an intermediate frequency, will be passed by pulse keyer 15 to pass them on to the rectifier and amplier apparatus 9| only within time intervals covf ered by the pulses from oscillator 92. As the time periods of signal pulses and pulses from oscillator 92 drift together until they overlap, signal pulse energy passes through keyer i5 and pulse energy is delivered through rectier and amplifier 9| to advance the pulses of oscillator 92. The more the signal pulses overlap into the pulses from v oscillator 92 the longer and stronger will be the pulses and Iche average D. C. current from 9| into oscillator 92 and the more oscillator 92 will be speeded up to tend to reduce the overlap. By

this means, after suits ole adjustments, oscillator 92 is synchronized by the signal pulses.

In this arrangement the power of energy from 9| to advance the phase and increase the frequency of oscillator 92 may be adjusted for optimum results. In addition, by employing dii'- ferent time constants in Si it is possible to obtain any desired rate of response of oscillator 92 to shifts of phase between signal pulses and pulses from 92. This time constant adiustment pro vides an equivalent control of averaging of the v synchronizing effect of signal pulses. equivaent,

to control of frequency selectivity for reducing the effects of noise arriving with the signals.

The connections from the pulse oscillator S2 -for supplying synchronizing pulses to the pulse' delayers of the multiplex receiver are also made across winding I3. each delayer being connected through a resistance like resistance ||5 to minimize reactions between delayers and the synchronizing system.

Fig. 11 illustrates a single pulse receiver for 't A I receiving modulated pulses of high frequency energy transmitted from a remote pulse type transmitter. This receiver includes an antenna which l is connected to the system through a transmission line |55, a detector circuit |5| 'vhich is shown as a crystal detector although it may be any suitable type of detecter, a pair of pulse amplifiers |52, a keyer ampler |53, another pulse ampliser |54, a detecter lss, an audio amplifier |51.

and a pulse oscillator |58 which operates in synchronism with the received pulses and controls the keyer amplifier |53.

In the operation of Fig. 1l, lzt us assume that this receiver is designed to receive ultra high frequency pulses having a percentage dura'lion of approximately 1% of the total time, repeated at a rate of 20,0()0 per second, and modulated in amplitude by speech waves at the transmitter. This 20.000 per second pulse rate is illustrative of :my suitable frequency above the highest moduaclon frequency. These ultra high frequency pulses are received in the antenna and passed on tu the crystal detector |5| over transmission line 25u. The detector |5| serves to provide in its output pulses of energy with the ultra high frequency carrier radio frequency current pulses. These pulses v is a saw-tooth wave although the voltage pulse 76 are then amplied in puise amplifiers |52. |53 and 2,478,919 i v l |54 and demodulated in detector ii. The pulse amplifiers |52. of course, have sufiicient over-all which operates in synchronism with and is controlled by the received pulses. This oscillator |58 Y: produces short pulses in the transformer |59 which discharge the condenser X and thereby block the pulse keyer amplier |58, the latter in turn being arranged to recover its operating potentials, as condenser X charges up again through its charging resistance, in suicient time for a succeeding pulse to start. Putting it in other words, it can be said that the oscillator |58 "shutters or gates" the amplier |53. The pulse amplifier |54 operates on the threshold principle. Grid rectification in this ampliier |54, due to signal pulses, biases the grid potential to such a value that weak currents such as may be produced by noise, do not produce'any output from the tube.

The coupling of signal pulses to oscillator |58 for accomplishing synchronizing is obtained from the screen grid current ci keyer tube |53, which responds to the signal pulses, and which reacts upon oscillator |58.

Fig. 12 shows another type of receiver which may be employed instead of the receiver of Fig. 11 for receiving amplitude modulated carrier wave pulses. The receiver ot Fig. 12 is an alternative to the receiver of Fig. 11 and both are equipped with the desirable feature of shutter-ing or "gating" the receiver synchronously with the transmitter, so that the receiver is operative solely at times when the signal pulses are due to arrive. In Fig. 12 the antenna is shown by way of example as a horn type of antenna for receiving ultra high frequency pulses of extremely short duration radiated by the remote transmitter. The received impulses are pwed from the antenna through transmissionline |50 to the detector l! which will produce direct current pulses. The direct current puise output from the detector i5| is passed on to three switching amplifiers |60 arranged in cascade, the output of which is passed on to a pulse integrator detector IBI which dernodulatcs the pulses and produces audio frequency current which is then amplified in audio amplier |62. The gating" or shuttering" of the receiver is effected by means of the pulse control switcher tLbe |55 and its associated elements. It should be noted that the control grid of tube |65 is connected to the output of the last puise switching ampliner |69. while the :creen grid circuits of the three pulse switching ampliiiers |80 are connected over a common lead to the anode oi' the tube |65. In the operation of the receiver of Fig. i2, tube |135. in the absence oi received pulses, is non-conductive. However, arrival of a signal pulse which passes through the receiver will causetube |65 to pass current thereby discharging the condensers in its anode circuit. This reduces the screen grid potentials of ampiiiiers IEU and makes them inoperative for e. time period I which is adjustable by adjusting the value o1 resistance through which the condensers are charged. This time period is adjusted to correspend to the time period between the received signal pulses. Thus the receiver is blocked during time periods between signal pulses. A pulse received on the receiving system and passed by the pulse switching amplifiers places a positive potential on the control grid of tube |65. thus rendering it momentarily conductive. The momentary conductivity of tube |65 lowers the screen potential on the three pulse switching amplier tubes |60, as a. result of which the receiver is rendered inoperative until a selected time later when another pulse is due to be received. The arrangement of condensers |66 and |61 in circuit with the tube |55 prevents the quick lowering of the screen potentials on the pulse switching ampliers until almost the end of the received pulse, thus allowing substantially the entire pulse to be used in producing output from the receiver. These condensers are, in e1- i'ect, a time delay circuit. Putting it in other words, the keyer or switcher tube |65 serves to discharge the screen potentials of the pulse switching ampliers |68 at each received pulse. These screen potentials, however, recover or assume their normal ivalues before the next pulse iS due to arrive.

It should be noted that tubes |60, in the absence of signal pulses, pass no current because of bias potential on their control electrodes. Therefore, pulses of the switcher do not pass energy on to the pulse integrator detector in the absence of a signal pulse.

What is claimed is:

l. In a multiplex communication system, s common pulse oscillator, a plurality of pulse modulators respectively coupled to the output oi' said pulse oscillator, a signaling source for each of said modulators for modulating a. characteristic of the pulses produced by said pulse oscillator, individual delay circuits respectively coupled to the outputs of said modulators and having auch constants that said delay circuits pass pulses of the same repetitiva. rate but which occupy sequentially dineren; timeA periods, the pulses from each delay cli cuit being short compared to the time interval between them, the percentage of time occupied by the pulses from all o! said delay circuits in each cycle of operations being a small fraction of the total time of said cycle, a radio frequency TTransmitter for sending said pulses, a. rfc #ver for receiving the pulses sent out by seid, transmitter, and a. plurality of channels at said receiver corresponding in number to the number of said pulse signalling sources, means at said recever for rendering said channel.: sequentially operative to receive the different signals from said signalling sources only at such rne periods when the signal pulses are due to arritfc, the time periods o! 0perativeness for the diffrent channels being dl!- ferent.

2. The combnation with a transmitter, of means coupled thereto for causing it to send out a plurality o! pulse transmissions each with its own modulation, the separate pulse transmissions being such that they do not coincide in time and all pulse transmissions in cach cycle ot operation occupy only a small percentage ot the total time of the cycle, said means including a common pulse oscillator from which the separate pulsa transmissions are derived, a plurality of modulator coupled to the output o! said oscillator, and

clay circuits coupled to the outputs of said Y modulators and having such constants as io pass pulses therethrough at non-overlapping intervals. and a receiver having associated therewith a plurality o! utilization clrcuits,one for each of said plurality of transmissions, and means at .said receiver for rendering said utiliza-l tion circuits operable in regular and synchronized sequence so as to permit said receiver to deliver a signal pulse to cach ultlzation circuit solely at a time period which can be occupied by the pulse to be utilized by the said receiver.

3. In a. multiplex communication system, a radio transmitter for generating ultra high frequency carrier waves, a pulse oscillator. a plurality of stations controlled by said pulse oscillator, each of said stations including a. modulator, a signalling source coupled to said modulator, and a delay circuit in the output of said modulator, the delay circuits in the different stations providing dlierent delays; a radio transmitter, and means coupling the outputs of said modulators to said radio transmitter for causing said transmitter to radiate a number of nonoverlapping pulse transmissions each composed of pulses of ultra high frequency waves of a duration not exceeding several microseconds, each of said pulse transmissions having its own modulation. the average repetition rate of each of said pulse transmissions being the same but higher than the highest modulation frequency. the percentage of time occupied by the pulses from all of said pulse transmissions in each cycleofoperations being a very small fraction of the total time of said cycle. and' a receiver having associated therewith a plurality of communication paths corresponding in number to the number of said pulse transmissions, and means at said receiver for conditioning said communication paths to be receptive at different times in synl chronized sequence and solely at time periods corresponding to the time spacing between the pulses of the different pulse transmissions.

4. In a pulse communication system wherein l intelligence is conveyed by means of time modulated pulses of high frequency energy, a receiver having an ampliller in the signal path. and means responsive to the received pulses for automatically keying said amplifier to be operative solely at time periods which may be occupied by the incoming pulses, said means including a pulse keyer vacuum tube normally biased to cut-oil'. a circuit for supplying the input circuit of said keyer tube with pulses representative of the receiver waves, and a feed back circuit between the output and input circuits of said keyer tube, said feedback circuit comprising a. rectifier, a. direct current amplifier for receiving the rectilied energy from said rectifier, and a pulse oscillator controlled by said direct current amplifier, said pulse oscillator normally operating at a pulse rate slightly different from the pulse rate of the incoming pulses but being cor-strained to operate at the pulse rate of the incoming pulses.

5. In a multiplex communication system. a pulse oscillator. a plurality of pulse signalling source: controlled by said pulse oscillator, each source including a pulse delay circuit, the pulse delay circuits of said sources having different time constants, whereby said sources transmit pulses of the same repetition rate but which occupy diilerent time periods, the pulses from each source being short compared to the time interval between them, the percentage of time occupied by :he pulses from all oi' said pulse signalling sources in each cycle o! operations being a very 14 small fraction of the total time of each cycle, aradio frequency transmitter foi sending said pulses. a receiver for receiving the pulses sent out by said transmitter. and a plurality o chanv v l Y nels at said receiver corresponding in number to the number of said pulse signalling sources, each of said channels including a pulse keyer, a pulse integrator and demodulator coupled t-n the output of said keyer, and an audio frequency amplifier coupled to the output of said integrator and demodulator, rizans at said receiver for' erati'leness 5er the different channels being diferent. s

6. A multiplex receiver for receiving a plurality of pulse transmissions of high frequency energy, comprising a lieterodyne receiver for ergy down to pulses of lower frequency energy, a plurality of communication channels coupled in common to the output of said receiver, each of said channels including a pulse keyer. a vacuum tube pulse integrator and demodulator circuit, and an audio frequency amplifier, a pulse delayer coupled to the irriut of each pulse kcyer, the different pulse delayers being adjusted to have different time delays, and a pulse synchronization system also coupled to the output of said hetersdyne receiver and responsive to the received pulses to produce pulses of the same repetition rate as the frequency of the received pulses, and a common connection from the in- Y puts of said pulse deiayers to said synchronization system, whereby said synchronization system conditions said channels to be operative in regular sequence and at different times registering solely wits: the time periods when signals are due to be received by the diierent channels.

7. In a pulse communication system wherein f intelligence is conveyed by means of pulses of high frequency energy and which pulses are short. compared to they time interval between them, a

receiver having an amplifier in the signal pathl a detector coupled to the output of said amplifier,'

a. pulse oscillator, means for synchronously operating said oscillator from the endings of the I periods which may be occupied by the incoming pulses. v

8. In a pulse communication system wherein intelligence is conveyed by means Aof pulses of high frequency and which pulses are short compared to the time interval between them, an antenna, a detector coupled to said antenna for converting said pulses of high frequency energy to direct current pulses. and amplifier in the signal path following said detector, and a pulse oscillator. means for synchronously operating said oscillator from the endings of the received pulses for automatically conditioning said amplifier t0 be receptive solely at time periods which may be occupied by the incoming pulses.

9. In a pulse communication system wherein intelligence is conveyed by means of amplitude modulated pulses of high frequency energy and which pulses are short compared to the time interval between them. an antenna, a detector coupled to said antenna for converting said pulses of high frequency energy to direct current pulses. a multi-stage amplifier in the signal path following sad detector, a pulse integrator detector following said multi-stage amplider, each stage of said amplifier comprising a screen grid tube having a polarizing potential applied to the screen lgrid thereof, and a normally non-conductive rallty of pulse transmissions of high frequency energy, comprising a heterodyne receiver for beating the received pulses of high frequency energy down to pulses of lower frequency energy, a plurality of communication channels coupled in common to the output of said receiver, each of said channels including a pulse keyer, a pulse integrator and demodulator, and an audio frequency amplifier, a pulse delayer coupled to the input of each pulse keyer, the different pulse delayers being adjusted to have diierent time delays, and a pulse synchronization system also coupled to the output of said heterodyne receiver and responsive to the received pulses to produce pulses of the same repetition rate as the frequency ofjhe received pulses, and a common connection from' the inputs of said pulse delayers to said synchronization system whereby said synchronization system conditions said channels to be operative in regular sequence and at different times registering solely with the time periods when signals are due to be received by the different channels, said pulse synchronization System including a pulse keyer vacuum tube normally biased to cutofI, and a feedback circuit between the output and input of said last pulse keyer vacuum tube, said-feedback circuit comprising a rectifier, and a pulse oscillator controlled by the rectied pulses.

11. In a multiplex communication system, a pulse oscillator, a plurality of pulse signalling sources controlled by said pulse oscillator and transmitting pulses of the same repetition rate but which occupy different times periods, the pulses from each source being short compared to the time interval between them, the percentage of time occupied by the pulses from all of said pulse signalling source in each cycle of operations being a very small fraction of the total time of each cycle, a radio frequency transmitter for sending said pulses. a receiver for receiving the pulses sent out by said transmitter, and a plurality of channels at said receiver corresponding in number to the number of said pulse signalling sources, each of said channels including a pulse keyer, a. pulse 16 integrator and demodulator coupled to the output of said keyer, and an audio frequency amplier coupled to the output of said integrator and demcdulator, means at said receiver for rendering said channels sequentially operative to receive the dilerent signals from said signalling sources only at such time periods when the signal pulses are due to arrive, the time periods of operativeness for the different channels being different, A'said last means including a pulse keyer vacuum tube normally biased to cut-olf, and a feedback circuit between the output and input of said lseyer vacuum tube, said feedback circuit comprising a rectifier and a pulse oscillator controlled by the rectiiied pulses.

12. In a pulse communication system wherein intelligence is conveyed by means of modulated pulses, a receiver having an amplifier in the path over which the received pulses may pass, said am plifier comprising a screen grid vacuum tube having a polarizing potential applied to the screen grid thereof,w and a normally non-conductive vacuum tube switcher having an input electrode coupled to the output of said amplier and an output electrode coupled to the screen grid of said amplifier, said switcher tube being momentarily rendered conductive by the pulses passed by said amplier to thereby reduce the screen potential on said amplifier, as a result oi which said receiver is rendered non-responsive for those periods between received pulses.

. CLARENCE W. HANSELL.

REFBENCES crrED The following references are of record in the ille of this patent:

. UNITED STATES PATENTS Number Name Date 717,767 Shoemaker Jan. 6, 1903 777,312 Shoemaker Dec. 13, 1904 1,573,983 Mathes Feb. 23, 1926 1,956,397 Nicolson Apr. 24, 1934 1,979,463 Goshaw Nov. 6, 1934 2,048,081 Riggs July 21, 1936 2,059,601 Peterson et al. Nov. 3, 1936 2,061,734 Kell Nov. 24, 1936 2,113,214 Luck Apr. 5, 1938 2,213,941 Peterson Sept. 3, 1940 2,241,078 Vreeland May 6, 1941 2,266,401 Reeves Dec. 16, 1941 2,275,224 Henroteau Mar. 3, 1942 2,313,906 Wendt Mar. 16, 1943 2,379,899 Hansell July 10, 1945 FOREIGN PA'I'ENIS Number Country Date 467,095 Great Britain June 7, 1937 521,139 Great Britain May 13, 1940 

